The present invention relates to radio communication technology, more particularly to technology effective for application to ramping up a control loop of a radio communication system, and specifically to technology effective for application to a radio communication system such as a portable telephone having a phase control loop for phase modulation and an amplitude control loop for amplitude modulation.
One of conventional schemes for radio communication apparatus (mobile communication apparatus) such as a portable telephone is GSM (Global System for Mobil Communication) which is employed in Europe. This GSM scheme uses a phase modulation mode called GMSK (Gaussian Minimum Shift Keying) which shifts the phase of a carrier in accordance with transmission data.
In recent portable telephones, an EDGE (Enhanced Data Rates for GMS Evolution) scheme has been proposed. The EDGE scheme has dual-mode communication functions, and relies on GMSK modulation to perform audio signal communications and on 3π/8 rotating 8-PSK (Phase Shift Keying) modulation to perform data communications. The 8-PSK modulation is such modulation that adds an extra amplitude shift to a phase shift of a carrier in the GMSK modulation. Since the 8-PSK modulation can send 3-bit information per symbol, in contrast with the GMSK modulation which sends 1-bit information per symbol, the EDGE scheme can achieve communications at a higher transmission rate as compared with the GSM scheme.
As one implementation of a modulation mode for imparting information on a phase component and an amplitude component, respectively, of a transmission signal, there is a conventionally known configuration called “polar loop” which involves separating a signal intended for transmission into a phase component and an amplitude component, subsequently applying feedback to the separated components through a phase control loop and an amplitude control loop, and combining the resulting components by an amplifier for outputting the combined components (for example, “High Linearity RF Amplifier Design” by Kenington, Peter B., p. 162, published by ARTECH HOUSE, INC. in 1979).